1. Field of the Invention
The invention provides a casting apparatus, a method for forming the casting apparatus, and a method for casting metal.
2. Related Art
Low pressure aluminum casting molds are typically provided by a pair of steel dies. The steel dies are mounted in a press above a sealed holding furnace containing the molten aluminum. The mold is typically connected to the holding furnace by riser tubes, which are also referred to as feed tubes or up tubes. Low pressure air is introduced into the holding furnace, and the pressure pushes the molten aluminum up the riser tubes and into the mold. The inside of the mold also has a low pressure, which sucks the molten aluminum up the riser tubes and onto the mold. Thus, the molten aluminum fills the mold from the bottom, and the combination of the pressure from the holding furnace and the pressure inside the mold can provide optimum mold filling. Another relatively low pressure, typically about 50 tons, is applied to the dies to keep the mold closed while molten aluminum fills the mold. The pressure is maintained for a predetermined amount of time as the aluminum solidifies in the mold to reduce porosity, shrink, and “no-fill” defects.
Cooling pipes can be used to convey water or compressed air and remove heat from the steel dies, which accelerates the shot-to-shot cycle time. Certain areas of the dies, such as the thickest areas, typically require more aggressive cooling to avoid shrink and/or porosity. Thermally isolated inserts can be drilled into the thickest sections of each die, and water can be pumped through the inserts to cool the thickest sections without cooling the bulk of each die. Ideally, the cooling time is set so that the aluminum solidifies quickly to avoid shrink porosity, but fills the mold without “no-fill” defects. However, the rate at which the dies are cooled by the cooling fluid is difficult to control, and sometimes the dies are overcooled, which leads to the “no-fill” defects and thus un-useable scrap.
In other cases, liquid cooling does not remove enough heat, so a blower fan is positioned at the back of the mold. However, fan cooling is very sensitive to ambient conditions and it is not spatially controllable. Therefore, fan cooling is not effective when only certain areas of the dies require additional cooling. A predictable and repeatable method for removing heat from concentrated areas of casting dies is still needed.